Christopher Howarth is a senior Political Analyst at the think tank Open Europe. Prior to Open Europe he worked as a Conservative Foreign Affairs Adviser and senior researcher to a Shadow Europe Minister. Follow Open Europe on Twitter.

The Coalition has already done some good work on the EU, the ‘referendum lock’ and the recently launched ‘audit’ of the EU’s influence on the UK to name two. However, the constraints of coalition government have tested the loyalties of Conservative MPs, party members and potential voters who wish to see substantial changes to the UK’s EU membership terms. As a result, Europe could damage the electoral coalition the Conservatives need to muster in order to win an outright victory. This is borne out by recent polling by Lord Ashcroft, which shows that 10% of Conservative voters say they would now vote for UKIP. Of course this may not happen, those who say they will vote UKIP may, when it comes to it, vote to keep the Labour party out. But it would be foolish to advocate complacency, not least as this also links to general trust in politicians. So what can be done?

Some talk of deals with UKIP, some talk of promises of a referendum, some talk of the need for a better defined Conservative vision for a post-2015 Government. These proposals all have specific problems and one major problem: Credibility. Would anyone (including in the first instance UKIP-inclined voters) believe them? Increasingly, the answer is no.

For this group of the electorate and party base, the Conservatives’ credibility on Europe has been hit by a series of forced and unforced errors. Whether perceived or real, the overselling of the Lisbon Treaty ‘cast iron’ guarantee, the revelations that before the election David Cameron’s policies may have been framed with Coalition in mind, the CCHQ prohibition on candidates campaigning on Europe, the opting in to EU crime and policing laws, lecturing the French and Germans on the need to create a Fiscal Union and now Cameron ruling out forever leaving the EU, all chip away at his credibility. In short, Cameron could promise to spend every waking moment committed to achieving new, improved EU membership terms, jump over the EU parapet, look back, and see his troops have opted to stay in the trenches.

Fortunately for David Cameron he has two great opportunities to address these concerns and reassure the electorate he means business, two opportunities where he can either act unilaterally or use a veto. Importantly both these opportunities come before the next election.

Firstly, David Cameron should use a quirk of the Lisbon Treaty to activate the 2014 block opt-out and repatriate around 130 EU crime and policing laws, rather than allowing them to fall under the jurisdiction of the European Court of Justice. He should then avoid squandering this gain by resisting pressure from within the coalition to opt back into them piecemeal. He should instead argue for either a better deal, under which the European Court has no jurisdiction in the UK over criminal law, or stay outside permanently.

Secondly, the UK should demand root and branch reform of EU regional policy, repatriating responsibility for regional funding to the UK and other richer member states. Limiting EU-managed regional funds to poorer countries would mean that 23 out of 27 EU countries pay less into the EU budget than at present, saving the UK £4bn net over seven years (in addition to the £8.7bn it currently gets back through the EU regional funds). This is achievable but Cameron must make it clear that he is prepared to veto the next multi-year EU budget, currently up for negotiation, in order to make this demand more credible.

These two measures would achieve several objectives simultaneously – a reduced EU budget contribution, repatriation of two areas of power from Brussels and limiting the powers of the EU judges – an early opportunity to get some ‘balls in the net’. If Cameron takes these two opportunities, this would be a substantial down payment for future electoral credibility which he will need when he promises a wider renegotiation with the EU. Without it, any future manifesto promise may be skilfully crafted but will not sway many voters’ minds.